Musnad Abu Ya'la al-Mawsili 115:336

Abu Musa narrated to us, Mu'adh bin Hisham narrated to us, my father narrated to me, from Qatadah, from Anas bin Malik, that the Messenger of Allah (ﷺ) used to go around to his wives during the hour of the night and the day, and they were eleven. He (the narrator) said: I said to Anas bin Malik, "Was he capable of that?" He said, "We used to say that he was given the strength of forty."